This invention is based on and claims priority to Japanese Patent Applications No. 2000-007571, filed Jan. 17, 2000, No. 2000-192251, filed Jun. 27, 2000 and No. 2000-204839, filed Jul. 6, 2000, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to an engine for a watercraft, and particularly to an improved exhaust system of an engine for a watercraft.
2. Description of Related Art
Personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries a rider and possibly one, two or three passengers. A relatively small hull of the personal watercraft commonly defines a riders"" area above an engine compartment. An internal combustion engine frequently powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the watercraft hull. The jet propulsion unit is located within the tunnel and is driven by a drive shaft. The drive shaft usually extends between the engine and the jet propulsion device, through a wall of the hull tunnel.
The rider""s area usually includes an elongated seat that extends along a longitudinal center line of the watercraft. The seat has a bench-like shape that the rider and passengers can straddle. Foot wells extend along side the seat. The rider and passengers straddle the seat in a tandem fashion with the rider and passengers"" legs positioned on the side of the seat and their feet placed within the foot areas.
Generally, the width of the seat not only provides an ample surface upon which the rider and passengers sit, but also provides space in which to locate an upper portion of the engine, including the engine""s exhaust and induction systems. U.S. Pat. No. 5,536,189 illustrates an exemplary engine arrangement beneath the seat with the overall width of the seat generally matching the overall width of the engine. The cylinder head, cylinder block, exhaust manifold, exhaust expansion chamber, carburetors, and air intake are all located between the side walls of the seat and beneath the upper cushion of the seat.
While the position of the riderxe2x80x94with his or her feet positioned wide apart and his or her legs straddling the seatxe2x80x94provides good stability, this stance reduces the ability of the rider to absorb with his or her legs impact forces as the watercraft bounds over wakes. In addition, some smaller riders with less height find it uncomfortable to sit in a position with their feet widely spaced apart when straddling the seat.
Additionally, two-cycle engines commonly power personal watercraft, as these engines have the advantage of being fairly powerful and relatively light and compact. One particular disadvantage of a two-cycle engine though, is emissions content. Two-cycle engines exhaust large quantities of carbon monoxide and various hydrocarbons. However, when steps are taken to reduce the emissions content of a two-cycle engine, other generally undesirable consequences result, such as an increase in the weight of the engine, cost of manufacture, and reduction of its power output.
Thus, four-cycle engines have now been proposed as the power plant for personal watercraft. These engines have the advantage of less hydrocarbon emissions than a two-cycle engine while maintaining a relatively high power output. It is therefore desirable to provide a small watercraft with a four-cycle engine in order to reduce exhaust emissions without significantly impacting the power output of the engine that powers the watercraft, or excessively increasing a width of the engine compartment.
According to one aspect of the present invention, an exhaust manifold for an internal combustion engine includes a first exhaust runner assembly having at least two exhaust runners. Each exhaust runner includes an inlet end configured to engage a corresponding exhaust port defined on one side of the engine. The exhaust manifold also includes a second exhaust runner assembly having an inlet end configured to engage at least one exhaust port defined on the side of the engine.
By constructing the exhaust manifold with two exhaust runner assemblies, the manufacture of the exhaust manifold is made easier. In the design and manufacture of exhaust manifold, a difficultly arises in shaping the exhaust runners so as to have approximately the same length. For example, known exhaust manifolds include a plurality of exhaust runners having inlet ends connected to a plurality of exhaust ports arranged in a substantially linear fashion. However, the outlet ends of the exhaust runners merge to define a single outlet passage of the exhaust manifold. Thus, the exhaust runners desirably are shaped differently from each other so as to have approximately the same length.
An exhaust manifold having exhaust runners with varying shapes is difficult to manufacture. In particular, some exhaust manifolds are monolithically cast from metal to improve a heat-resistant characteristic. Thus, an exhaust manifold having more than two exhaust runners with varying shapes is particularly difficult to manufacture. Further, where the exhaust manifold is water-cooled, the varying shapes of the exhaust runners provides an additional difficulty in manufacturing a cooling jacket disposed thermal communication with the exhaust manifold. For example, due to the high heat environment of the exhaust manifold, an outer wall of such a cooling jacket is also made from a cast metal, monolithically formed with the exhaust manifold.
Thus, by constructing the exhaust manifold, in accordance with the present aspect of the invention, with first and second exhaust runner assemblies, the exhaust runners and any associated cooling jackets can be manufactured more easily.
According to yet another aspect of the present invention, a water vehicle includes an internal combustion engine having an engine body and a plurality of exhaust ports defined along a first side of the engine body. The water vehicle also includes an exhaust system having a plurality of individual exhaust passages extending from the exhaust ports, respectively. The individual exhaust passages terminate in the vicinity of a forward end of the engine.
As noted above, known exhaust manifolds typically include a plurality of exhaust runners having inlet ends attached to a corresponding number of exhaust ports defined in a substantially linear fashion on one side of an engine body. The outlet ends of the exhaust runners merge to define a single outlet passage of the exhaust manifold. In order to provide each of the exhaust runners with approximately the same length, the exhaust runners are shaped differently from one another. For example, an exhaust runner communicating with an exhaust port disposed adjacent a longitudinal end of the engine body can be shaped substantially linearly. An exhaust runner communicating with an exhaust port disposed near the middle of the engine body may be curved such that the overall length of the exhaust runners is approximately equal. However, some applications for internal combustion engines cannot provide large amounts of free space adjacent the desired position of the engine body.
For example, in the art of personal watercraft, the rider""s seat is typically positioned directly above the engine compartment, with the rider straddling the engine compartment during operation. While the position of the riderxe2x80x94with his or her feet positioned wide apart and his or her legs straddling the sea xe2x80x94provides good stability, this stance reduces the ability of the rider to absorb with his or her legs impact forces as the watercraft bounds over wakes. In addition, some smaller riders with less height find it uncomfortable to sit in a position with their feet widely spaced apart when straddling the seat. Thus, the overall width available for the engine in such a watercraft is limited.
By providing the exhaust system of the water vehicle with a plurality of individual exhaust passages that terminate in the vicinity of a forward end of the engine, the variations in the shapes and accounts of the individual exhaust passages can be more easily accommodated. Thus, the upstream portion of the exhaust system connected to the exhaust ports, usually referred to as the exhaust manifold, can be made smaller.
According to yet another aspect of the present invention, an exhaust system for an internal combustion includes an exhaust conduit extending from the exhaust ports to an exhaust discharge for discharging exhaust gases to the atmosphere. The exhaust conduit also includes a first exhaust passage extending through a high point defining a highest elevation in the first exhaust passage. The first exhaust passage is defined by a plurality of individual exhaust passages having inlet ends configured to engage a plurality of exhaust ports defined on a first side of an engine body. The individual exhaust passages extend to the high point.
According to a further aspect of the present invention, an exhaust system for an internal combustion engine includes a first exhaust passage extending from exhaust ports of the engine and through a first elevation and a second elevation. The first elevation is lower than the exhaust ports, and the second elevation is at least as high as the exhaust ports. By configuring the exhaust passage to extend from exhaust ports of an internal combustion engine and through such a first and second elevation, the exhaust passage aids in preventing water from traveling upstream through the exhaust system to the exhaust ports.
According to another aspect of the present invention, an exhaust system for an internal combustion engine of a watercraft includes an exhaust manifold communicating with the at least one exhaust port of the engine. An exhaust conduit extends from the exhaust manifold to a first elevation defining a high point in the exhaust conduit when the watercraft is inverted. The exhaust conduit also extends to a second elevation defining a high point in the exhaust conduit when the watercraft is upright. By configuring the exhaust conduit to extend through such a first and second elevation, the exhaust system aids in preventing water from traveling upstream through the exhaust system when the watercraft is upright and inverted.
According to yet a further aspect of the present intention, an exhaust system for an internal combustion engine includes an exhaust passage having a plurality of individual exhaust gas conduits communicating with a plurality of exhaust ports of the engine. The individual exhaust gas conduits are connected to each other and include first and second ends. The exhaust system also includes a flexible cooling jacket member having first and second ends and defining a cooling jacket around an exterior of the individual exhaust gas conduits. The first end of the cooling jacket member is connected to the first end of the individual exhaust gas conduits. The second end of the cooling jacket member is not directly connected to the second end of the individual exhaust gas conduits.
By providing a flexible cooling jacket member to the exhaust system, wherein one end of the flexible cooling jacket member is connected to a portion of the exhaust system and the second end is not directly connected, assembly of the exhaust system is made easier. For example, when a technician is connecting another portion of the exhaust system to the individual exhaust gas conduits as well as the cooling jacket member, these components are aligned before fasteners can be secured. Thus, by leaving one end of the flexible cooling jacket member free from the individual gas conduits, alignment of this portion of the exhaust system with another portion is made easier.
According to another aspect of the present invention, an exhaust system for an internal combustion engine includes at least first and second exhaust passages communicating with first and second exhaust ports defined on an engine body of the engine. The first and second exhaust passages include first and second lengths, respectively. The first and second exhaust passages also have first and second diameters, respectively. The first length is greater than the second length, and the first diameter is greater than the second diameter.
According to yet another aspect of the present invention, an exhaust system for an internal combustion engine includes at least first and second exhaust passages communicating with first and second exhaust ports defined on the engine body of the engine. The first and second exhaust passages include first and second links, respectively. A first restriction is disposed at an outlet end of the first exhaust passage, and the first length is greater than the second length.
According to a further aspect of the present invention, an exhaust system for internal combustion engine includes at least first and second exhaust passages having outlet ends. The first and second exhaust passages also include inlet ends communicating with first and second exhaust ports defined by engine body of the engine Each of the first and second exhaust passages include a balance passage aperture defined between the inlet and outlet ends thereof. The exhaust system also includes a cooling jacket in thermal communication with at least the first and second exhaust passages. A balance passage connects the balance passage apertures of the each of the first and second exhaust passages. At least a portion of the cooling jacket being upstream of the balance passage.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.